Aqueous fractionation yields chemically stable lupin protein isolates J.A.M. Berghout, C. Marmolejo-Garcia, C.C. Berton-Carabin, C.V. Nikiforidis, R.M. Boom, A.J. van der Goot ⁎ Food Process Engineering Group, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands abstract article info Article history: Received 16 December 2014 Accepted 24 March 2015 Available online 28 March 2015 Keywords: Lupin protein Lipid oxidation Protein oxidation Aqueous fractionation The chemical stability of lupin protein isolates (LPIs) obtained through aqueous fractionation (AF, i.e. fraction- ation without the use of an organic solvent) at 4 °C or 20 °C was assessed. AF of lupin seeds results in LPIs containing 2 wt.% oil. This oil is composed of mono- and poly-unsaturated fatty acids and the isolate may thus be prone to lipid and protein oxidation. Lipid and protein oxidation marker values of LPIs obtained at 4 °C and at 20 °C were below the acceptability limit for edible vegetable oils and meat tissue protein; the level of lipid oxidation markers was lower at 20 °C than at 4 °C. The fibre-rich pellet and the protein-rich supernatant obtained after AF also had lower levels of oxidation markers at 20 °C than at 4 °C. This is probably the result of a higher solubility of oxygen in water at lower temperature, which could promote lipid oxidation. The differences between fractions can be explained by the differences in their composition; the fibre-rich pellet contains polysac- charides that potentially have an anti-oxidative effect, while the protein-rich supernatant is rich in sulphur-rich proteins that may scavenge metal ions and free radicals from the aqueous phase. Additionally, the differences in solubility of metal ions and metal-chelating properties of protein at pH 4.5 and pH 7.0 explain the higher level of oxidation in the LPI at pH 4.5 compared with the LPI at pH 7.0. The application of a heat treatment to reduce oxidation decreased the protein and oil recovery values, and increased oxidation values above the acceptability limit. Therefore, AF at 20 °C is the most suitable process to obtain chemically stable LPIs. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Lupin seeds are rich in protein, which makes this crop a promising candidate for plant-based, high-protein foods. Dehulled lupin seeds of Lupinus angustifolius L. contain about 39–44 wt.% protein, about 7–10 wt.% oil and are further composed of dietary fibres, sugars, minerals and water (Bähr et al., 2014). L. angustifolius L. is a sweet lupin, implying that the alkaloid levels are well below the critical value of 200 mg/kg for lupin-based foodstuffs, and thus not toxic to humans (Small, 2012). Lupin seeds are an attractive alternative to soy- bean because the seeds have similar protein content, nutritive value and both oils are rich in unsaturated fatty acids (Cerletti & Duranti, 1979; Duranti, Consonni, Magni, Sessa, & Scarafoni, 2008; Sbihi, Nehdi, Tan, & Al-Resayes, 2013). An advantage of lupin is that it can be grown in moderate climates and on poor soils (Sujak, Kotlarz, & Strobel, 2006). Lupin protein isolation is generally performed through wet fraction- ation processes (Lqari, Vioque, Pedroche, & Millan, 2002; Wäsche et al., 2001), in which aqueous fractionation is preceded by defatting using an organic solvent. In a previous paper we introduced an alternative fractionation process, referred to as purely aqueous fractionation (AF), which is a sustainable alternative to conventional wet fractionation be- cause the oil extraction step is omitted and thereby the use of organic solvents (Berghout, Boom, & van der Goot, 2014). It is worth mentioning that the solubility and water holding capacity of the lupin protein isolate (LPI) obtained with AF was similar to that obtained with conventional wet fractionation (Berghout et al., 2014). However, a consequence of AF is the presence of some lupin oil during the fractionation process and in the resulting products. The composition of lupin oil has already been studied (Sbihi et al., 2013; Schindler et al., 2011), and includes a substantial amount of polyunsaturated fatty acids (PUFAs), which is an asset from a nutritional point of view, but also makes the oil sensitive to oxidation. Hence, the presence of oil could give rise to increased oxi- dation of both oil and protein in the obtained fractions. Oil in lupin seeds is present in the form of oil bodies that have a size around 0.1–0.5 μm (Tzen, 1992), which are stabilized by phospholipids and a dense protein complex. This outer structure provides physical and chemical protection against environmental stresses, such as moisture variation, temperature fluctuation and the presence of oxidative reagents (Chen, McClements, Gray, & Decker, 2012; Gray, Payne, McClements, Decker, & Lad, 2010; Karkani, Nenadis, Nikiforidis, & Kiosseoglou, 2013). Lipid oxidation is one of the prime mechanisms of quality deteriora- tion in foods, as it leads to the formation of unpleasant flavours and odours and to the loss of nutritional value (Velasco, Dobarganes, & Márquez-Ruiz, 2010). Mono- and especially poly-unsaturated fatty acids, are related with health benefits (Siriwardhana, Kalupahana, & Moustaid-Moussa, 2012) and it is thus important that these remain non-oxidized. Due to physical–chemical changes during storage and fractionation (high moisture content) and the presence of oxygen, Food Research International 72 (2015) 82–90 ⁎ Corresponding author. Tel.: +31 317 480852. E-mail address: atzejan.vandergoot@wur.nl (A.J. van der Goot). http://dx.doi.org/10.1016/j.foodres.2015.03.039 0963-9969/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres